1. Field of the Invention
The present invention relates to a stage device having a plurality of stages, and more particularly, to a stage device for use in an exposure apparatus.
2. Description of the Related Art
In recent years, various types of stage devices for use in exposure apparatuses have been developed in order to meet a demand to increase the speed and accuracy of exposure.
U.S. Pat. No. 2004/0126907 A1 discloses a stage mechanism that simultaneously performs exposure and alignment with two stages. It further discloses a stage device having a surface motor, in which only a stage with a wafer placed thereon is moved on a base in the X- and Y-directions. In this stage device, the stage is supported in the Z-direction in a non-contact manner by a levitation force based on a Lorentz force produced by energizing coils in the base. Japanese Patent Laid-Open No. H08-028564A discloses that a gas bearing is provided between the base and the stage to support the stage in such a manner.
In the stage mechanism, it is preferable that bases be separately disposed, respectively, in an exposure region and an alignment (measurement) region so that vibration due to movement of one of two stages does not adversely affect the other stage. In this case, when the stages are swapped between the exposure region and the alignment region, they pass over the space between the bases.
However, in a case in which a gas bearing is used to support the stages in the Z-direction, when a gas supply restriction of the gas bearing lies in the space between the separate bases, a sufficient levitation force is not ensured somewhere. If the levitation force is insufficient, the stages may touch the bases while moving above the bases.
When the stages are supported in the Z-direction by the application of a current to the coils, as in US Patent No. 2004/0126907 A1, a great force is needed to support the weights of the stages, and much heat is thereby generated by the coils. However, heat from the coils may deform components. And, when laser interferometers are used to measure the position of the stage, air fluctuates because of temperature nonuniformity in a measurement optical path. In both cases, accuracy is affected seriously.